If you want to be able to write adf files to a floppy on a PC you need "catweasel" I think. Otherwise you can modify certain pc-drives to be Amiga compatible. I would start searching for retired PCs and rip the floppys out and then do a google search on the part number to see if it's a suitable candidate for modding.
Here is some other good information on the topic:
http://www.amigaforever.com/kb/13-118
